The scale of the election gamble confronting Gordon Brown is revealed today in a Guardian ICM poll showing Labour and the Tories neck and neck, closing an eight-point gap since the Guardian polled at the start of the conference season.
The poll was conducted after David Cameron had completed his much-hailed conference speech in Blackpool. But Labour aides said last night they had identified the source of the surge as the Tory announcement on inheritance tax and the promise that only millionaires would have to pay death duties.

The poll shows the main two parties level after a summer and autumn in which Labour appeared to be pulling away from Mr Cameron, a trend that prompted Mr Brown's aides to urge him to call a November 1 poll next week.
Last night Labour MPs in marginal seats were said to be very nervous about a snap election. The new ICM poll, from a sample of 1008 people, shows Labour on 38%, Conservatives 38% and Liberal Democrats 16%. Tory support has climbed six points since last month's Guardian/ICM poll, returning to the level it reached a year ago at the end of the party conference season. Today's figure is also the Conservative party's highest ICM score since March, when it held a strong lead over Labour as Tony Blair prepared to depart.

Two other tests of opinion last night, one for YouGov conducted for Channel 4 and another by Populus for the Times, also reveal a dramatic tightening of the Labour lead. YouGov shows the Labour lead cut from eleven to four points with Labour on 40%, the Conservatives on 36% and the Lib Dems on 13%. Other parties are on 11%. Populus puts Labour on 39% (down two points), Tories 36% (up five) and Lib Dems 14% (down two).

The Brown camp was not last night signalling that plans for the election will be definitely pulled in the wake of these polls, but his election team was suggesting more strongly than before that its private polling in the key marginal seats showed the Conservatives doing comparatively well.

Brownites are aware the prime minister will look weak if he pulls back now but believe it would be a short-term setback. A key factor, they say, is whether the Brown team would have enough time in a relatively short election campaign to conduct what is described as a search-and-destroy mission on the Tory tax-and-spend plans.

No 10 indicated last night that the government's comprehensive spending review and pre-budget report will be published on Monday, regardless of whether the election is called.

Advocates of an election were pointing out that the Tories were bound to secure a bounce at the end of the conference season. But the findings caused nerves among some MPs. Derek Wyatt, MP for Sittingbourne and Sheppey - Labour's third most marginal seat, with a majority of 79 - said: "No one wants it. I think we have to take it on the chin and move on."

Andrew Dismore, MP for Hendon, said: "It's a bit like the mobilisation of world war one: once you start, nobody can stop it. Nobody really wanted a war but it happened. I think what we have to say is does anybody really want it? And if not, let's take a deep breath."

There is comfort for advocates of the election in that much of the Tory recovery appears to come at the expense of the Lib Dems, rather than Labour. Support for Labour has fallen only two points since last month's Guardian/ICM poll, and at 38% is higher than when Tony Blair left office.

That suggests Labour's core vote has remained solid despite the Conservatives' high-profile week, which will comfort those around Mr Brown urging him to call an election now.

Backing for the third party has dropped four points to 16% - a six-year low in the ICM series and a potential crisis for Sir Menzies Campbell whether or not an election is called. Backing for smaller parties has also dropped one point to 7%, substantially lower than it was earlier this year.

The question of how the parties would perform in an immediate general election remains finely balanced. Regional differences and the impact of local campaigning mean that Labour could not be certain to gain an overall majority, although academic estimates suggest that Labour would win 350 seats on today's figures, an overall majority of around 20.

That is much lower than the 66 it achieved in 2005. New boundaries have already reduced this to a notional 48 seats and anything below this level would call into doubt a decision to hold an early general election.

The Conservatives could expect to gain strongly if today's figures were translated into seats, with one academic estimate suggesting the party would win 244 seats. But any Liberal Democrat recovery during the campaign could eat into Tory support, and boost Labour's majority.

Mr Cameron exploited Mr Brown's dilemma by writing to him yesterday asking for the prime minister to allow meetings between opposition parties and senior civil servants to begin immediately.

Such talks are commonplace in the months before the election to prepare civil servants for a change of government. Mr Cameron said Mr Blair had agreed to authorise such meetings from January 2009.

· ICM interviewed a random sample of 1,008 adults aged 18+ by telephone between October 3 and 4 2007. Interviews were conducted across the country and the results have been weighted to the profile of all adults. ICM is a member of the British Polling Council and abides by its rules.

Last wednesday, yougov gave labour a 13% lead. Almost all polling data since June has just been hot air so I'm not going to lose that much sleep over this - I'll wait and see how the figure changes over the weekend.

Also, even if those figures represented the eventual votes cast it would still give labour a small majority if you measure the change in share proportionally over individual constituencies and consider how most of the votes are being taken from an imploding liberal democrats.